1. Field of the Invention
This invention relates to color management implemented in computers, and in particular, it relates to gamut mapping models useful in conjunction with Windows Color System.
2. Description of Related Art
Windows Color System (WCS) is the color management scheme used by Microsoft's Windows Vista operating system. Minimum Color Difference (MinCD) and Hue Mapping are two gamut map models (GMMs) in WCS that correspond to different rendering intents established by the ICC (International Color Consortium) for color gamut mapping. In the MinCD GMM, which is equivalent to the ICC calorimetric intent, “In-gamut colors are left unchanged. For out-of-gamut colors, lightness and chroma are adjusted by finding the point in the destination gamut that has the minimum color distance from out-of-gamut input points.” WCS Gamut Map Model Profile Schema and Algorithms, http://msdn2.microsoft.com/en-us/library/ms536899.aspx, pp. 6-7. The goal of MinCD is to provide the most “calorimetrically” correct output by minimizing the difference between the target and the destination colors. Colors that are inside both gamuts are not modified, colors from the target gamut that are not located within the destination gamut are moved to the closest boundary location on the output gamut. According to the above-cited document, “The MinCD GMM is suitable for mapping graphics and line art containing ‘logo’ colors (spot colors), logo color gradients with some out-of-gamut colors, and for the final stage of proofing transforms. While the MinCD GMM could be used for photographic images that are entirely within the destination gamut, it is not recommended for general rendering of photographic images. The mapping of out-of-gamut colors to colors on the destination gamut surface can result in unwanted artifacts, such as tone or chroma irregularities in smooth gradients that cross the gamut boundary.” Id. at p. 6.
For WCS Hue Mapping, which is equivalent to the ICC Saturation rendering intent, the goal of the procedure is to maximize the chroma (or saturation) of the output image at the expense of the hue angle. The calorimetric accuracy of the output image color itself is not as important as the “vividness” of the output image. According to the above-cited document, Hue Mapping “first adjusts the hue of the input color value. Then it simultaneously adjusts the lightness and chroma, using a shearing mapping. Finally, it clips color value to make sure it is within gamut.” Id. at pp. 17-22.